ZZ plants are among the most popular low-maintenance houseplants because they tolerate drought and low light conditions and thrive in a wide range of humidity levels.
The ideal humidity for optimum ZZ plant health is 40-50%. Moderate moisture levels in the air can help them preserve moisture in their leaves without inviting unwanted pests or plant pathogens. This range is also recommended for most homes to prevent mold and mildew.
This article will help you understand a ZZ plant’s humidity requirements and how to tailor your indoor garden to match them.
ZZ Plants: An Overview
ZZ plants (Zamioculcas zamiifolia) naturally grow in tropical East and South African regions. They can be found in humid coastal areas or dry inland forests.
Coastal areas are typically hot and humid (~80%), with abundant rainfall during the wet season. The loose soil helps cancel out the negative effects of heavy rains and high humidity by draining the excess moisture away from the roots.
Variegated ZZ plant cultivars are abundant in tropical areas because the more intense sunlight makes the markings more distinct. They’re more tolerant to higher humidity and a few hours of direct sun than their solid-colored relatives.
On the other hand, inland forests are cool and dry (10-60%) with less frequent rainfall. The dense tree canopies protect low-growing plants from sunburn and dehydration.
Darker-colored ZZ plants, including the Raven, typically grow in these areas because too much sunlight can make the leaves appear lighter or even burn them.
Humidity Requirements
In the wild, the roots and rhizomes can survive very dry or humid conditions, but the leaves may turn yellow or brown and dry. Therefore, it’s crucial to maintain a suitable humidity level around your indoor ZZ plants.
Ideal Humidity Range
ZZ plants do best at humidity levels ranging from 40-50%, especially at moderate temperatures around 75 °F (24 °C). Both temperature and humidity affect your plant’s ability to transpire.
Transpiration is a crucial process. The release of moisture through the leaves in vapor form works like a vacuum to draw moisture and nutrients from the soil through the roots, facilitating the movement of nutrients along different parts of the plant.
Since ZZ plants are accustomed to hot and humid or cool and dry conditions, there are two other scenarios in the home environment to watch out for:
- Cool and humid environments caused by using humidifiers indoors in winter can reduce the plant’s transpiration rate. The excess moisture (sap) within the leaves can invite pests. If there’s water in the soil and the root pressure is high, your plant will release droplets through its leaves (guttation). The droplets will leave white stains on the foliage as they dry and can be burdensome to clean.
- Hot and dry environments in the summer can increase the transpiration rate and risk of dehydration. If left unaddressed, the leaves may turn brown and crisp.
In addition to the physiological effects on the plant, humidity levels can affect soil conditions:
- The reduced transpiration rate at high humidity can keep the soil moist for extended periods. The wet surface can invite molds or fungus gnats. That’s why using a soil mix with excellent drainage is important.
- Low humidity can dry out the soil more quickly. If not properly rehydrated, the soil can become hydrophobic over time.
ZZ plants thrive in a humidity range of 40-50%, which optimizes their transpiration rate. Experts and researchers also suggest maintaining indoor humidity between 30 and 50% for human health.
While moisture-loving plants prefer higher humidity levels of 70-80%, this can negatively impact human health. Humidity levels above 60% can create conditions conducive to the growth of various plant and human pathogens on moist surfaces.
Therefore, when grouping your ZZ plants with moisture-loving plants in the same spot in your home garden, it’s best to keep the humidity at 60% for balance.
Measuring Humidity
You can measure the humidity using a built-in thermostat with a hygrometer. The digital reading will show you the temperature and relative humidity levels.
Some spots in your house may be more humid than others, such as the kitchen or bathroom.
You can use a portable or handheld hygrometer to measure the humidity more accurately around your plants. Handheld hygrometers are user-friendly. They usually have probes, which can easily detect air moisture and temperature and transmit the data to the screen.
Pro tip: Beginner gardeners with a few houseplants may not need to invest in portable devices. Because ZZ plants are versatile, it’s easy to ignore humidity levels when caring for them. They’ll do just fine if you can maintain moderate humidity in your home.
I’ll discuss some tips on how to find the right environment for your ZZ plant later in the article.
Signs of Inadequate Humidity
Trivia: Absolute humidity is the amount of water vapor in the air regardless of temperature. Relative humidity, however, is the actual amount of vapor in the air versus the total amount it can hold at a given temperature.
You should refer to the relative humidity (expressed in percentage) for the plant environment. ZZ plants usually don’t mind different or fluctuating humidity levels.
Problems start showing only when other stressors are affecting your plant, including the following:
- Overwatering
- Underwatering
- Intense sunlight
- High or low temperatures
High Relative Humidity
High relative humidity (over 70%) means the air is close to saturation, and there’s little vapor required to fill the air, so your plant transpires less.
If your ZZ plant is overwatered and the humidity is high, you may notice the following signs:
- White water stains on the leaves: The vapor can condense over the cool leaf surface into water droplets. The stains can also come from the liquid released by the plant through guttation.
- Mold on the moist soil surface: The excess water in the soil can’t evaporate quickly enough, giving mold time to reproduce. This is common if you tend to overwater your plant.
- Fungus gnats hovering over your plant: This can happen after watering your plant deeply and the top 2-3 inches (5-7.6 cm) of the soil remains moist. Gnats may also be attracted to the mold on the soil and lay their eggs, which will hatch in 4-6 days. The larvae can then feed on the ZZ roots and rhizomes.
Low Relative Humidity
Low relative humidity (below 30%) means the air is dry and will suck out the moisture from plant leaves through transpiration.
Coupled with intense sunlight, high temperatures, and/or underwatering, you’ll see the following signs (in ascending order based on severity):
- Yellow leaf tips that eventually turn brown and crisp
- Leaf scorch (brown, sunburnt marks with yellow margins)
- Leaf curling or wrinkling
- Leaf drop
Detecting the early signs of stress, such as leaf discoloration, and addressing them promptly can prevent severe damage to your ZZ plant.
Troubleshooting and Remedies
The first step to fix the problem is to address the more severe issues, such as watering problems, lighting problems, and incorrect temperatures. Adjusting the humidity will then help improve your ZZ plant’s condition.
Here are some tips:
- Increase the local humidity by placing the pot over a pebbled tray with water or switching on a humidifier near your indoor garden. Alternatively, group your ZZ plant with other houseplants that share similar environmental requirements.
- Decrease the humidity by switching on a dehumidifier, opening the windows, or turning on a fan near your plants. You can also prune or divide your plants for less dense foliage with better air circulation.
Optimizing Humidity
You can prevent humidity-related problems around your ZZ plant with the following considerations:
Proper Placement
You can enjoy your ZZ plant’s low-maintenance requirements by choosing an appropriate location for them in your home.
Here are some tips for the proper placement:
- Choose a spot that receives bright indirect light for at least 8 hours a day. It can be a corner 4-8 feet (1.2-2.4 m) away from a bright eastern, southern, or western window. Without direct sunlight or high temperatures, low humidity can hardly dehydrate a drought-tolerant ZZ plant.
- Choose a well-ventilated spot with stable temperature and humidity. Good air circulation can repel moisture-loving pests and prevent mold or mildew from growing on the potting mix or leaf surface.
- Avoid spots next to drafty or sunny windows or doors. Frequent and drastic temperature fluctuations and intense sunlight can stress your plant, and improper humidity can worsen the damage.
- Keep your plant away from the direct path of cold air from air conditioners or hot air from heating vents.
- Don’t place your ZZ plants inside laundry rooms or bathrooms. The temperature and humidity fluctuations can result in wilting, curling, or leaf drops. The light conditions in these rooms may also be too low, even for ZZ plants.
Adjusting to Seasonal Changes
Indoor humidity can fluctuate with the changing seasons and aggravate the damage to stressed ZZ plants. Adjusting the humidity around your plant with the light, temperature, and watering frequency can help keep the leaves vibrant all year round.
Summer Care
ZZ plants are drought-tolerant, but some summers can be too hot and dry. Move the pot a few feet (~0.6 m) farther from a bright window, or hang sheer curtains to filter the light. This should slightly reduce the transpiration rate and prevent dehydration.
If the conditions become too dry and the leaf tips turn yellow, you may need to increase the watering frequency or switch on a humidifier.
If you live near the coast and summers in your area can be hot and humid, you can keep the windows open to improve air circulation. Keep your plant in moderate light conditions to prevent leaf scorch.
Winter Care
Cold winter air can feel dry. Heaters like furnaces absorb the cold air and heat it through the coils, removing moisture and resulting in lower humidity.
Place a humidifier next to your indoor garden to maintain the optimum humidity to ensure your evergreen plants remain in the best shape even in winter.
Spring and Fall
During mild seasons like spring and early fall, check the humidity using a hygrometer.
You can slowly transition from a humidifier or dehumidifier to a pebbled tray with water until the relative humidity indoors becomes optimal. Then, you can remove the pebbled tray from your indoor garden.
Companion Plants
Grouping your ZZ plant with other houseplants can create a low-maintenance microenvironment wherein all plants can benefit.
Here are some excellent companions for ZZ plants in your indoor garden:
Air Plant
The air plant doesn’t grow in soil. It absorbs moisture and nutrients from the air and can help reduce humidity (albeit not significantly). It can hang above your ZZ plants because they share similar light, humidity, and temperature requirements.
Nerve Plant
The nerve plant is a moisture-loving, low-light plant that can benefit from growing alongside other houseplants because the low indoor humidity is often not enough. Its colored venations can also provide interest alongside the solid-colored ZZ leaves.
Parlor Palm
If you want a more tropical feel inside your home, parlor palms make excellent low-light companions for ZZ plants. They also thrive at around 50% humidity.
Snake Plant
The snake plant shares similar requirements as ZZ plants, including light, temperature, humidity, and watering frequency. According to Feng Shui, its effect on harmony complements the good fortune of ZZ plants.
Final Thoughts
Although ZZ plants can tolerate dry or humid conditions, maintaining the optimal level can ensure the leaves remain vibrant. Incorrect humidity is often a secondary cause that can aggravate your plant’s stress symptoms.
ZZ plants are resilient and will bounce back after correcting the underlying cause of stress or damage. However, they’re slow growers, so it can take time for new shoots to grow.
Maintaining moderate humidity levels (40-50%) can help boost your plant’s nutrient absorption through transpiration and improve the metabolic processes necessary to grow a healthy foliage.
Please leave a comment if you have questions or valuable insights about ZZ plant care. Don’t forget to subscribe for more gardening tips!
